A solar cell with a property of semiconductor converts a light energy into an electric energy.
A structure and principle of the solar cell according to the related art will be briefly explained as follows. The solar cell is formed in a PN-junction structure where a positive (P)-type semiconductor makes a junction with a negative (N)-type semiconductor. When a solar ray is incident on the solar cell with the PN-junction structure, holes(+) and electrons(−) are generated in the semiconductor owing to the energy of the solar ray. By an electric field generated in an PN-junction area, the holes(+) are drifted toward the P-type semiconductor, and the electrons(−) are drifted toward the N-type semiconductor, whereby an electric power is produced with an occurrence of electric potential.
The solar cell can be largely classified into a wafer type solar cell and a thin film type solar cell.
The wafer type solar cell uses a wafer made of a semiconductor material such as silicon. In the meantime, the thin film type solar cell is manufactured by forming a semiconductor in type of a thin film on a glass substrate.
With respect to efficiency, the wafer type solar cell is better than the thin film type solar cell. However, in the case of the wafer type solar cell, it is difficult to realize a small thickness due to difficulty in performance of the manufacturing process. In addition, the wafer type solar cell uses a high-priced semiconductor substrate, whereby its manufacturing cost is increased.
Even though the thin film type solar cell is inferior in efficiency to the wafer type solar cell, the thin film type solar cell has advantages such as realization of thin profile and use of low-priced material. Accordingly, the thin film type solar cell is suitable for a mass production.
The thin film type solar cell is manufactured by sequential steps of forming a front electrode on a glass substrate, forming a semiconductor layer on the front electrode, and forming a rear electrode on the semiconductor layer. In this case, since the front electrode corresponds to a solar ray incidence face, the front electrode is made of a transparent conductive material, for example, ZnO. With the large-sized substrate, a resistance is increased in the front electrode made of the transparent conductive material, thereby causing the increase in power loss.
Thus, a method for minimizing the power loss has been proposed, in which the thin film type solar cell is divided into a plurality of unit cells, and the plurality of unit cells are connected in series. This method enables the minimization of power loss caused by the resistance of the transparent conductive material.
Hereinafter, a related art method for manufacturing a thin film type solar cell with a plurality of unit cells connected in series will be described with reference to the accompanying drawings.
FIGS. 1A to 1F are cross section views illustrating a related art method for manufacturing a thin film type solar cell with a plurality of unit cells connected in series.
First, as shown in FIG. 1A, a front electrode layer 20a is formed on a substrate 10, wherein the front electrode layer 20a is made of a transparent conductive material, for example, ZnO.
Next, as shown in FIG. 1B, predetermined portions of the front electrode layer 20a are removed through the use of laser-scribing method, thereby forming a front electrode 20.
As shown in FIG. 1C, a semiconductor layer 30a and a transparent conductive layer 40a are sequentially formed on an entire surface of the substrate 10.
As shown in FIG. 1D, a contact portion 35 for connection of the electrodes is formed by removing predetermined portions of the semiconductor layer 30a and transparent conductive layer 40a through the use of laser-scribing method, thereby forming a semiconductor layer pattern 30 and a transparent conductive layer pattern 40.
Next, as shown in FIG. 1E, a rear electrode layer 50a is formed on the entire surface of the substrate 10.
As shown in FIG. 1F, separating portions 45 are formed by removing predetermined portions of the rear electrode layer 50a through the use of laser-scribing method, thereby dividing the solar cell into a plurality of unit cells.
According as the solar cell is divided into the plurality of unit cells, and the unit cells are connected in series, the resistance of front electrode is not increased even in the large-sized substrate, thereby preventing the problem of power loss.
However, the related art method for manufacturing the thin film type solar cell necessarily requires the laser-scribing process three times. This may cause the following problems.
First, large amounts of particles may generate due to the performance of laser-scribing procedures. The generated particles may cause the problems such as a contamination of substrate and a short of device. In order to overcome these problems generated due to the particles, a cleaning procedure is additionally performed after performing the laser-scribing procedure. However, the additional cleaning procedure makes the entire process complicated, and causes the increase of manufacturing cost since it requires a cleaning apparatus.
Second, if laser is excessively supplied to the desired layer due to the inappropriate control of laser irradiation and exposing time, the lower layer positioned under the desired layer may be scribed.